More bhp...

[rjkflyer]

Love all this "does my car make 414bhp...?"

Just tried some 1/4 mi tests, as today is a 1013mbar and 15 deg C day - nice conditions, aside a bit windy but at least was from the side so not too bad.

Got repeatedly similar numbers on three runs (within 0.05 sec on time and 0.1 mph on speed).

13.69sec 105.9mph

Car weight is about 3900 lbs with fuel as currently filled plus driver plus various shyte in the car.

95% stock car - only exhaust flap mod and K&N.

In the calculator on one of the dyno threads, that gives me a bhp at crank of 412. (The 224 times cube root of bhp/weight)

Doing the calc with 3900lbs and 414bhp provided 1/4 mile trap of 106mph and ET of 13.3 secs

All looks close enough for government work... Less expenses of course...

What WILL make you all laugh is that I did this with the iPhone application as seen at http://www.bunsentech.com/

Now make of all that what you will. Perhaps I won't (a) buy the Racelogic fancy unit after all, and (b) certainly not worry about the power output.

And, it all seemed and felt ****ing quick.

[Dom81]

That looks awesome - I'm downloading tonight

I would use VAG-COM, but we're a mac family and the only one that runs windoze has a knock sensor so knackered that it shuts down if you so much as breathe on it. It's fine (just) for checking fault codes, but gives up on the move!

[SR71]

Which just goes to show that using 1/4 mile times is open to interpretation as well...

Using the formulas on http://www.stealth316.com/2-calc-hp-et-mph.htm and your figures you get:

LRT "Best fit" formula: 371hp using 105.9mph & 3900lbs
OR 349hp using 13.69 & 3900lbs

Patrick Hale formula: 361hp using 105.9mph & 3900lbs
OR 300hp using 13.69 & 3900lbs

Geoffrey Fox formula: 381hp using 105.9mph & 3900lbs
OR 374hp using 13.69 & 3900lbs

The LRT "Best Fit" has the best R^2.

IMHO, inspite of the bleating about how accurate using drag times is for calculating power, when we're talking about ~30hp deficit on quoted power, you're looking at a ~0.2 sec increment.

Is Audi going to take more notice of a complaint along the lines of "My dyno graphs show a 30hp deficit!" or "My car runs 0.2 secs slower than it should!"?

Anyones guess I suppose.

But I do know that after 3 drags in a row, my clutch stinks, so I know which route I'd rather take to prove the point.

PS: rjkflyer

Okay weighed the car today.....4180lbs with me in it !
Just under 1/2 tank of fuel

So calculate horsepower
13.3 1/4 mile time
104 trap speed
4180lbs
= 359.07 hp

I think the saloon is only ~130lbs lighter than the Avant?

[ArthurPE]

the car weighs 3900 loaded?

most weigh >3900 fueled, no driver...

[PetrolDave]

What sort of accuracy are people looking for in power figures? Remember nothing you measure is absolute, it always has an error margin.

The post from SR71 shows a +/- 10bhp difference using the different formulae - that a 2.7% variation.

Seems that even the best dynos have a +/- 5% margin of error in torque.

Let's assume a 5% margin of error on measurements - that means a power figure of 414 +/-20 (i.e. 394 to 434) bhp and a torque figure of 317 +/-15 (i.e. 302 to 332) lb ft would be an indication of an engine meeting exactly meeting spec.

[SR71]

Bloody hell guys, you're picking the figures that suit your argument.

If you use the ET, the difference is between 300-374!

The last 6 runs my car has done using the GTechPro RR and a 12" rollout:

13.098@110
13.064@111
13.171@110
13.229@109
13.313@109
13.393@108

I made no note of ambient conditions at the time, nor have I measured tail-wind assistance, nor slope etc etc... I don't think I changed "pitch correction" factor either...

I wouldn't dare fire that data off to Audi in defence of an argument, as its not controlled in any sensible fashion.

Just a bit of fun.

But now you're all going to tell me my car is fine.

Tell me something new. I've always said I'm reasonably happy with its performance.

But if I go and do some runs with a 0" rollout and the ET's/speeds all change by ~-0.5 secs & ~3mph, what will you say, because that'll have a big effect on the numbers?

Similarly, Arthur's results prove nothing except that he possibly fiddled the figures (like he is accusing everyone else of doing), or that he has a good car.

Collectively, however, the fact is the car covers its internals in sludge, because the oil isn't up to spec, the separator doesn't work, this has a demonstrable effect, although possibly small, on power (look at the graphs!) and it isn't right. But then, we've only ever been arguing about small percentages, even for "healthy" cars. In my own opinion, this in conjunction, with a lack of control over the dependent variables at your average dyno, is responsible for the discrepancies...

This is what Audi should address.

I'm sorry but I shouldn't have to wait until my valves start failing to seal until Audi address the issue. Judging by karl's experience, you've got about 20K miles to play with before that happens....which is right where my car is...

[P_G]

What happened to Karl's car and at what mileage? Must have missed that somewhere!

[Dom81]

MRC found a non-sealing valve whilst decoking - 20k from memory

[PetrolDave]

I'm sorry but I shouldn't have to wait until my valves start failing to seal until Audi address the issue. Judging by karl's experience, you've got about 20K miles to play with before that happens....which is right where my car is...

My car has done over 30k miles and doesn't have any noticeable loss of power in day-to-day use, the fuel consumption is much the same as it always has been, the oil consumption is the same as it always has been, the exhaust smoke happens when it always has and to the degree that it always has - so as far as I can tell there's no sign of loss of compression.

[P_G]

Ditto and my car has done 48k miles now. And there isn't anything on APM's car either from I remember him and JonP writing about. May just be Karls.

[bingboybri]

gees guys..... you are scaring the bejeasus outa me here......
im in the market for a rs4 but its looking more like ill be sticking with bmw m3s at this rate with all the talks of under powered cars and leaking struts and the like .........give me some good news about rs4s...

[P_G]

gees guys..... you are scaring the bejeasus outa me here......
im in the market for a rs4 but its looking more like ill be sticking with bmw m3s at this rate with all the talks of under powered cars and leaking struts and the like .........give me some good news about rs4s...

They don't have as many problems as M3's? Just from reading the BMW boards.

[Dom81]

give me some good news about rs4s...

No-one here wants to sell (although some, unfortunately, have to). Those who move on don't find a thing to match the RS4, to the extent that some end up re-buying. We're (almost all) a very happy bunch!

The struts have extended warranty by the way...

[DavidRoss]

gees guys..... you are scaring the bejeasus outa me here......
im in the market for a rs4 but its looking more like ill be sticking with bmw m3s at this rate with all the talks of under powered cars and leaking struts and the like .........give me some good news about rs4s...

Just what i was thinking when i came here to research RS4's.... have just read lots of problems and it has pretty much put me off buying one for now at least. Found the Rs4 i tested to be no quicker than my remapped but otherwise standard 2008 s3. I do know that forums tend to highlight problems more but DRC issues, massively underpowered and engines clogging up or what not has scared the s**t out of me, and it seems vey common, not just the odd complaint. If I purchased the one i've been looking at (£34K) I would be really p***d off let alone if I dropped £50k on one

[P_G]

FFS, are you for real? Given these supposed issues, like Dom81 said, we all still have our cars and there is perhaps only one or two cars that could replace it in the C63.

DRC is covered under warranty, carbon deposists have not been proven to cause significant power loss or damage to the engine and they have not been accurately proven to be underpowered.

There is not better pound for pound car out there bar perhaps an M5 V10 and then they do have massive running costs compared to our RS4's